Steve wrote: > > All, > > Background; > > I'm being consumed by a hybrid failure suffered by one of my > subcontractors. The cause of failure is silver bridging two gold > conductors metallized on an alumina substrate. In DC mode, one conductor > is at -5.5V, the other at +28V. The conductor spacing is ~146 microns. > > The silver is from an epoxy die attach on the +28V conductor. The silver > bridging the conductors is a combination of deposited (workmanship) and > dendrite (electrochemical) formation. The deposited silver is half on > the -5.5V wire-bond land and half bridging the alumina. Dendrites form > the rest of the bridge across the alumina. Dendrites are also observed > *IN* the silver epoxy die attach. > > Now for the question; > > 1)Understanding the conditions necessary for silver (electrochemical) > migration, how could silver dendrites form *IN* the silver epoxy? There > shouldn't be any potential difference *IN* silver epoxy. > > 2)How could the +28V silver migrate out of the epoxy die attach across > the +28V gold metallization then across the alumina? The silver die > attach was completely within the +28V gold metallization. Again, no > potential difference to "steer" migration. Oddly, an identical config in > the same hybrid did have +28V silver epoxy squeeze out into the alumina > bridging 1/3 the way to -5.5V. No silver migration observed there. > > If any one can help, I can be reached @ steve.r.anderson @ trw.com > (remove the spaces before & after the @). > > I can post optical & SEM/EDX images to our ftp site but they will be > removed after 24 hrs. > > ############################################################## > TechNet Mail List provided as a free service by IPC using LISTSERV 1.8c > ############################################################## > To subscribe/unsubscribe, send a message to [log in to unmask] with following text in the body: > To subscribe: SUBSCRIBE TECHNET <your full name> > To unsubscribe: SIGNOFF TECHNET > ############################################################## > Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional information. > For the technical support contact Dmitriy Sklyar at [log in to unmask] or 847-509-9700 ext.311 > ############################################################## Hi Steve- Silver is one of the few metals that will form "single crystal" wire-like filaments when subjected to stress. In fact, in the literature, it was reported back in the '30 forming filaments on the same conductor/plated surface. I suspect the epoxy is expanding due to thermal stress which stresses the silver and then the silver forms the filaments. Silver has always been a reliability concern inelectronic assemblies. Hope this helps. Ralph -- Ralph Hersey Ralph Hersey & Associates 3885 Mills Way Livermore, CA 94550-3319 PHN: 510.454.9805 FAX: 510.454.9805 e-mail: [log in to unmask] ############################################################## TechNet Mail List provided as a free service by IPC using LISTSERV 1.8c ############################################################## To subscribe/unsubscribe, send a message to [log in to unmask] with following text in the body: To subscribe: SUBSCRIBE TECHNET <your full name> To unsubscribe: SIGNOFF TECHNET ############################################################## Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional information. For the technical support contact Dmitriy Sklyar at [log in to unmask] or 847-509-9700 ext.311 ##############################################################